Crystal structures of seven mixed-valence gold compounds of the form [(R (1) R (2) R (3)PE)(2)Au(I)](+)[Au(III) X (4)](-) (R = tert-butyl or isopropyl, E = S or Se, and X = Cl or Br).

During our studies of the oxidation of gold(I) complexes of tri-alkyl-phosphane chalcogenides, general formula R (1) R (2) R (3)PEAuX, (R = tert-butyl or isopropyl, E = S or Se, X = Cl or Br) with PhICl(2) or elemental bromine, we have isolated a set of seven mixed-valence by-products, the bis-(tri-alkyl-phosphane chalcogenido)gold(I) tetra-halogenidoaurates(III) [(R (1) R (2) R (3)PE)(2)Au](+)[AuX (4)](-). These corres-pond to the addition of one halogen atom per gold atom of the Au(I) precursor. Com-pound 1, bis-(triiso-propyl-phosphane sulfide)-gold(I) tetra-chlorido-aur-ate(III), [Au(C(9)H(21)PS)(2)][AuCl(4)] or [( (i) Pr(3)PS)(2)Au][AuCl(4)], crystallizes in space group P2(1)/n with Z = 4; the gold(I) atoms of the two cations lie on twofold rotation axes, and the gold(III) atoms of the two anions lie on inversion centres. Compound 2, bis-(tert-butyl-diiso-propyl-phosphane sulfide)-gold(I) tetra-chlorido-aurate(III), [Au(C(10)H(23)PS)(2)][AuCl(4)] or [( (t) Bu (i) Pr(2)PS)(2)Au][AuCl(4)], crystallizes in space group P1 with Z = 4; the asymmetric unit contains two cations and two anions with no imposed symmetry. A least-squares fit of the two cations gave an r.m.s. deviation of 0.19†à . Compound 3, bis-(tri-tert-butyl-phosphane sulfide)-gold(I) tetra-chlorido-aurate(III), [Au(C(12)H(27)PS)(2)][AuCl(4)] or [( (t) Bu(3)PS)(2)Au][AuCl(4)], crystallizes in space group P1 with Z = 1; both gold atoms lie on inversion centres. Compound 4a, bis-(tert-butyl-diiso-propyl-phosphane sulfide)-gold(I) tetra-bromi-doaurate(III), [Au(C(10)H(23)PS)(2)][AuBr(4)] or [( (t) Bu (i) Pr(2)PS)(2)Au][AuBr(4)], crystallizes in space group P2(1)/c with Z = 4; the cation lies on a general position, whereas the gold(III) atoms of the two anions lie on inversion centres. Compound 4b, bis-(tert-butyl-diiso-propyl-phosphane selenide)gold(I) tetra-bromido-aurate(III), [Au(C(10)H(23)PSe)(2)][AuBr(4)] or [( (t) Bu (i) Pr(2)PSe)(2)Au][AuBr(4)], is isotypic with 4a. Compound 5a, bis-(tri-tert-butyl-phosphane sulfide)-gold(I) tetra-bromido-aurate(III), [Au(C(12)H(27)PS)(2)][AuBr(4)] or [( (t) Bu(3)PS)(2)Au][AuBr(4)], is isotypic with compound 4a. Compound 5a, bis-(tri-tert-butyl-phosphane sulfide)-gold(I) tetra-bromido-aurate(III), [Au(C(12)H(27)PS)(2)][AuBr(4)] or [( (t) Bu(3)PS)(2)Au][AuBr(4)], crystallizes in space group P1 with Z = 1; both gold atoms lie on inversion centres. Compound 5b, bis-(tri-tert-butyl-phosphane selenide)gold(I) tetra-bromido-aurate(III), [Au(C(12)H(27)PSe)(2)][AuBr(4)] or [( (t) Bu(3)PSe)(2)Au][AuBr(4)], is isotypic with 5a. All Au(I) atoms are linearly coordinated and all Au(III) atoms exhibit a square-planar coordination environment. The ligands at the Au(I) atoms are anti-periplanar to each other across the S⋯S vectors. There are several short intra-molecular H⋯Au and H⋯E contacts. Average bond lengths (à ) are: P-S = 2.0322, P-Se = 2.1933, S-Au = 2.2915, and Se-Au = 2.4037. The complex three-dimensional packing of 1 involves two short C-H(methine)⋯Cl contacts (and some slightly longer contacts). For 2, four C-H(methine)⋯Cl inter-actions combine to produce zigzag chains of residues parallel to the c axis. Additionally, an S⋯Cl contact is observed that might qualify as a 'chalcogen bond'. The packing of 3 is three-dimensional, but can be broken down into two layer structures, each involving an S⋯Cl and an H⋯Cl contact. For the bromido derivatives 4a/b and 5a/b, loose associations of the anions form part of the packing patterns. For all four compounds, these combine with an E⋯Br contact to form layers parallel to the ab plane.